1. Field of the Invention
The present invention relates generally to a bicycle rear wheel axle positioning device which is mounted onto a rear portion of a bicycle frame and capable of easily adjusting positions of the rear wheel axle.
2. The Prior Arts
A conventional transmission system for a bicycle includes a chain wheel and a rear sprocket. The chain wheel is disposed at a front portion of a bicycle frame and connected to two cranks which are respectively connected with two pedals. The rear sprocket is disposed to a side of a hub and fixed to an axle of a rear wheel. A drive chain is connected between the chain wheel and the rear sprocket. When the cyclist treads the pedals, the chain wheel rotates to drive the rear sprocket by the drive chain. Because the rear sprocket is fixed to the axle of the rear wheel, the rear wheel is rotated to move the bicycle forward. A derailleur system includes multiple rear sprockets in different diameters and the drive chain is shifted between the rear sprockets to get the desired speed.
Because the drive chain is a closed loop, when mounting the drive chain to the chain wheel and the rear sprocket, the distance between the chain wheel and the rear sprocket has to be shortened, so as to easily mount the drive chain to the chain wheel and the rear sprocket. Then the distance between the chain wheel and the rear sprocket is adjusted to tighten the drive chain, such that the drive chain does not disengage from either of the chain wheel or the rear sprocket. Because the chain wheel is fixed to the front portion of the bicycle frame, it usually moves the rear sprocket to adjust the distance between the chain wheel and the rear sprocket. Referring to FIG. 1, each of the chain stays of the conventional bicycle is connected to a wheel axle positioning device “A”. The wheel axle positioning devices “A” each have a groove “A1” which can be horizontal, inclined or any pattern. Two ends of the axle B1 of the rear wheel “B” is movable along the two grooves “A1”, respectively. After the drive chain is assembled, the axle B1 is moved to a position of the wheel axle positioning devices “A” to tighten the drive chain and nuts “C” are used to fix the axle B1 to the wheel axle positioning devices “A”.
The connection between the wheel axle positioning devices “A” and the axle B1 is fixed by the friction when the nuts C are tightly installed. After being used for a period of time, the wearing between the nuts C and the wheel axle positioning devices “A”, and the wearing between the groove A1 and the axle B1 may cause gaps which mean the nuts C need to be fastened again to tighten the connection. Moreover, the axle B1 in the groove A1 may rotate relative to the groove A1, which changes the central position of the axle B1.